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# To Determine the Concentration of a Limewater Solution.

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Introduction

To Determine the Concentration of a Limewater Solution. Balanced Equation: Ca(OH)2 + 2HCl CaCl2 + 2H2O I have decided to use 25cm3 of Ca(OH)2 as this is the standard measurement of alkali to dilute in a titration. Concentration of HCl needed: n=m/M Grams of calcium hydroxide = 1g RAM of Ca(OH)2 = 74.1 Moles of Ca(OH)2 = 1/74.1 = 0.014moldm-3 This means to use around 25cm3 of acid to dilute the Ca(OH)2, we need a concentration of around 0.03moldm-3. This is because of the 1:2 ratio needed for a complete reaction. This ratio means that one mole of Ca(OH)2 will react with two moles of HCl. Volume of HCl needed: Molarity of acid = 2M Approx. concentration of acid needed = 0.03moldm-3 Final volume of solution = 500cm3 n=CV therefore V=n/C Volume of Acid = 2/0.03 = 66.7 500/66.7 = 7.5cm3 This means that we can round up the volume of HCl to make the measurement errors smaller. ...read more.

Middle

1. Set up a burette with the hydrochloric acid you have just made. 2. Use a bulb pipette to transfer accurately 25cm3 of the calcium hydroxide solution into a clean 250cm3 volumetric flask. 3. Add 4-5 drops of methyl orange indicator solution to the flask. 4. Note the initial reading on the burette. 5. Run the acid from the burette into the flask about 1cm3 at a time, swirling the flask after each addition. Observe the colour of the indicator. 6. Stop the addition of acid when a permanent colour change occurs and note the final reading on the burette. 7. Using the burette readings, calculate an approximate volume of acid required to react completely with the Ca(OH)2. 8. Repeat steps 2, 3 and 4. 9. Add the acid quickly to the flask up to a few less centimetres less than the volume estimated in step 7, and then add the acid one drop at a time until the indicator just begins to change colour. ...read more.

Conclusion

The acid or the alkali could damage your eyes if it comes into contact with them. Also, when using the acid you should try to avoid skin contact as strong acids can be corrosive and although the acid you will be using is relatively dilute it may still cause some irritation if contact occurs. When filling the burette with hydrochloric acid you should have it on the floor and your eyes above the top of the funnel so that if you do spill any it will not go in your eyes. You should also make sure that the tap on the burette is closed before pouring in any acid. When using the bulb pipette you should use the valve device that goes on top of the pipette that will suck up the solutions for you. The calcium hydroxide is also corrosive to the eyes and skin so you should also be careful when handling it. Both solutions can be irritating to the respiratory system so you should try not to inhale the fumes. ...read more.

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